16,804 research outputs found
On the choice of parameters in solar structure inversion
The observed solar p-mode frequencies provide a powerful diagnostic of the
internal structure of the Sun and permit us to test in considerable detail the
physics used in the theory of stellar structure. Amongst the most commonly used
techniques for inverting such helioseismic data are two implementations of the
optimally localized averages (OLA) method, namely the Subtractive Optimally
Localized Averages (SOLA) and Multiplicative Optimally Localized Averages
(MOLA). Both are controlled by a number of parameters, the proper choice of
which is very important for a reliable inference of the solar internal
structure. Here we make a detailed analysis of the influence of each parameter
on the solution and indicate how to arrive at an optimal set of parameters for
a given data set.Comment: 14 pages, 15 figures. Accepted for publication on MNRA
NIR Luminosity Function of Galaxies in Close Major-Merger Pairs and Mass Dependence of Merger Rate
A sample of close major-merger pairs (projected separation kpc, band magnitude difference mag) is selected from the matched 2MASS-2dFGRS catalog of Cole et al.
(2001). The pair primaries are brighter than mag. After
corrections for various biases, the comparison between counts in the paired
galaxy sample and counts in the parent sample shows that for the local `M*
galaxies' sampled by flux limited surveys, the fraction of galaxies in the
close major-merger pairs is 1.70. Using 38 paired galaxies in the
sample, a band luminosity function (LF) is calculated. This is the
first unbiased LF for a sample of objectively defined interacting/merging
galaxies in the local universe, while all previously determined LFs of paired
galaxies are biased by mistreating paired galaxies as singles. A stellar mass
function (MF) is translated from the LF. Compared to the LF/MF of 2MASS
galaxies, a differential pair fraction function is derived. The results suggest
a trend in the sense that less massive galaxies may have lower chance to be
involved in close major-merger pairs than more massive galaxies. The algorithm
presented in this paper can be easily applied to much larger samples of 2MASS
galaxies with redshifts in near future.Comment: Accepted by ApJL, 16 pages, 2 figure
On The Determination of MDI High-Degree Mode Frequencies
The characteristic of the solar acoustic spectrum is such that mode lifetimes
get shorter and spatial leaks get closer in frequency as the degree of a mode
increases for a given order. A direct consequence of this property is that
individual p-modes are only resolved at low and intermediate degrees, and that
at high degrees, individual modes blend into ridges. Once modes have blended
into ridges, the power distribution of the ridge defines the ridge central
frequency and it will mask the true underlying mode frequency. An accurate
model of the amplitude of the peaks that contribute to the ridge power
distribution is needed to recover the underlying mode frequency from fitting
the ridge.
We present the results of fitting high degree power ridges (up to l = 900)
computed from several two to three-month-long time-series of full-disk
observations taken with the Michelson Doppler Imager (MDI) on-board the Solar
and Heliospheric Observatory between 1996 and 1999.
We also present a detailed discussion of the modeling of the ridge power
distribution, and the contribution of the various observational and
instrumental effects on the spatial leakage, in the context of the MDI
instrument. We have constructed a physically motivated model (rather than some
ad hoc correction scheme) resulting in a methodology that can produce an
unbiased determination of high-degree modes, once the instrumental
characteristics are well understood.
Finally, we present changes in high degree mode parameters with epoch and
thus solar activity level and discuss their significance.Comment: 59 pages, 38 figures -- High-resolution version at
http://www-sgk.harvard.edu:1080/~sylvain/preprints/ -- Manuscript submitted
to Ap
Tomografia passiva costiera (TOMPACO). Inversion results with passive data - phase 3
Rep 02/03 - SiPLAB
28/March/2003This report shows the acoustic inversion results obtained
on the INTIFANTE’00 data set, Events II, IV, V and VI
Real-time environmental inversion using a network of light receiving systems
This paper reports preliminary environmental
inversion results of acoustic data collected simultaneously at two receiving systems during the RADAR’07 sea trial. These receiving systems have communication
capabilities that allow for transfering acoustic and telemetric data to a base station with processing capabilities in order to produce environmental estimates during the acoustic experiment. During a large part of the experiment estimates on the temperature field appear to agree with concurrent ground truth data
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